Stir butter, ginger, and salt in a small bowl; set aside. Score a 1/4-inch border on each pastry. Score a crosshatch pattern within border. Brush each with butter mixture, then sprinkle each with 1/4 teaspoon sugar. Bake until crisp and lightly browned, 16 to 18 minutes. Transfer to a wire rack to cool.

Top 4 pastry squares with 1 scoop sorbet. Layer each with another pastry square and scoop of sorbet. Top with remaining pastry squares. Garnish with berries and mint.